This invention relates to crosslinked polymers, and in particular, to crosslinked polymers which form water-swellable, water-insoluble foams.
Linear polyalkylenepolyamines are rendered water-insoluble through the addition of diisocyanates at a temperature between about 30.degree. C. and about 200.degree. C., using techniques disclosed in U.S. Pat. No. 4,087,413. Unfortunately, the resulting water-insoluble products are prepared either in neat form or in the presence of a suitable solvent. Reactions of amines with diisocyanates are disclosed in U.S. Pat. No. 4,177,038. However, it is typically necessary to prepare such products under essentially anhydrous conditions because isocyanates moieties are hydrolyzed rapidly by water to yield substituted ureas.
More recently, as disclosed in U.S. patent Ser. No. 585,744, filed Mar. 2, 1984, now U.S. Pat. No. 4,478,938, issued 10/23/84 linear polyalkylenepolyamines can be crosslinked in a non-anhydrous environment by contacting the polyalkenepolyamine with a polyisocyanate in an aqueous liquid at a specific pH and subjecting the mixture to high shear. Although essentially water-insoluble gels are prepared, these gels find limited uses.
In view of the fact that known processes provide gelled materials, it would be highly desirable to provide a process for efficiently preparing stable, water-swellable but water-insoluble foams.